Unit-heater control



July 1, 1930. w sw T 1,768,805

7 UNIT HEATER CONTROL Original Filed June 10, 1927 INVENTOR HAROLD W.SWEATT A TTORNEYE Patented July 1, 1930 UNITED STATES PATENT OFFICEHAROLD w. SWEATT, OF MINNEAPOLIS, MINNESOTA, ASSIGNOR T0 MINNEAPOLIS-HONEYWELL REGULATOR COMPANY, OF MINNEAPOLIS, MINNESOTA, A CORRORA- TIONOF DELAWARE UNIT-HEATER CONTROL Original application filed June 10,1927,8erial No. 197,987. Divided and this application filed October 27,

1928. Serial No. 815,563.

This invention relates generally to improvementsin heat regulatingdevices and is partlcularly directed to the control of a circuit havinga power driven fan, which fan is 7 associated with a heating unit suchas a radiator for the purpose of circulating air heated by the radiator.

This application is divisional of m copending application, Serial Number19 ,987, filed June 10th, 1927 for unit heater control.

In the usual systems in which the fan of a unit heater is controlled bya room thermostat, it happens that the fan is frequently operated whenthe radiators or heaters are cold. Inasmuch as these heaters aresometimes arranged adjacent the outer wall of a building and, inasmuchas conduits are often provided so that cold outside air may be deliveredto the radiator, operation of the fan when the radiator is cold wouldresult in a cold draft being forced into the building, or the fan wouldcreate a cold draft which is also undesirable. Moreover, inhot watersystems, or in steam systems in which the drainage is imperfect, it mayhappen that if the fan starts at a time when there is no heat in aradiator, the water of condensation may be frozen which might result andsometimes does result in cracking of the radiator. Also under theseconditions, when thawing takes place, a considerable amount of damagemay be done by leaking water.

The main object of the invention is to provide means which will obtainand allow operation of the fan, as the result of temperaturefluctuations in a roomonl when the heater has reached a predeterminedtemperature. Another object of the invention is to provide a very simpleelectrically operable means for controlling the operation of the fan.Another and more specific object is to provide a single relay, operableand controllable through two devices, one dominating control of theother, one a thermostatically responsive device arranged in the room,and the other a device responsive to fluctuations in heat supply at theheater. The arrangement is such that the room device can only operate tocause energization of the fan motor when both heater and room devicesare closed.

will not start unless the room device is fully closed. v

Features of the invention include the broad idea of controlling the fanof a unit heater by use of a single switch controlling, or relay device,to positively prevent running of the fan when the heater is cold, alongwith the detailed arrangement of the elements of the apparatus forobtaining the results set forth herein. I

The figure of the drawing diagrammatical- 1y represents the system, withmotor not runnlng.

To show one application of the invention the following construction isillustrated:

The fan motor is indicated at 1 and this motor is opposingly arranged insuch relation to a radiator 13" as to circulate air heated by theheater. In this instance, a circuit is provided which includes atransformer the primary coil of which is indicated at 2 and thesecondary coil of'which is indicated at 3. A single relay is used andhas an armature 11 having a contact 6 cooperable with contact 5 of thehigh voltage circuit. Conductor 7 con nects one side of the motor 1 withone side of the main line 25, and conductor 8 connects at the oppositeside of the motor with the contact 5, the opposite side 26 of the mainline is connected by conductor 9 with the contact 6 of the armature 11.The relay coil is indicated at 10 and is connected with one side of thesecondary 3 by conductor 15. The armature 11 is provided with a contact12 cooperable with contact 13. A thermostatically responsive room devicehas a movable member 1' having inthis instance two electricallyconnected elements, respectively 1" and 1' respectively engageable withtwo contacts 6-10. These elements 1"'r are sequentially engageable withthe contacts b w. Element 7 is first to engage and last to-disengage,and

element 1" is last to engage and first to disenf her 21, which member inthis instance has a pair of elements insulated from one another, andrespectively designated R and R. These elements are engageablerespectively with contacts B-W, and make sequentiallyR' first and Rlastand in reverse order when breaking.

The coil 10 and contact 12 are connected by conductor 17 to contact B ofthe radiator device. The opposite side of the secondary side of thetransformer 8 is connected by conductor 16 with contact lV ot theradiator device. Contact 13 is connected by conductor 18 with member 7of the room device. It will be noted that the elements 1, 1 are notinsulated. Contact 5 of the room device is connected by conductor 19with element R of the radiator device, and contact w of the room deviceis connected by conductor 20 with the element R of the radiator device.

The connections in the secondary circuit are so arranged between theroom and the heater device of the relay, that the room device can onlyoperate to close the relay and obtain energization of the fan motor,when both elements are making with respective contacts Z w, and thisenergization can only take place when both elements of the radiatordevice are engaging respectively With the contacts B-lV of that device.It will be further noted that one element (7 and R) of each device actsto maintain a closed circuit for the holding contact 1213.

It will be understood that the element 1" of the room device can be of abimetallic structure, or of any structure which will make it responsiveto bend in opposite directions following the fluctuations intemperature. It will be further understood that the element 21 may beeither a bimetallic element or a Bourdon tube or other device which canbe afi'ected when the radiator is hot to move in one direction and whenthe radiator is cooled to move in the opposite direction.

Operation The diagram shows the system inoperative, with both room andradiator devices having their elements out of contact. In this position,therefore, the fan is not running because the radiator is sufiicientlycool to have caused breaking at both contacts, and the room thermostatis sufficiently warm to have also opened or broken both its contacts.

To show how the device operates to prevent energization of the fan motorwhen the heater is cold, let it be assumed, with the device positionedas shown in the illustration, that the room device cools sufiiciently tomake at 1"-w. Under these conditions, the coil 10 cannot be energized toclose the motor control switch because the elements RR are both spacedaway from their contacts. Let us suppose that, on continued cooling ofthe room thermostat, the element 7 contacts I).

It is evident that no circuit can pass through the conductor 19, elementB because R-B are out of contact. Let it be supposed that while 1 w and7b are together, the radiator device heats sufiiciently to make at R\V.Even under these conditions no current can pass (conductor 20, R, V, 16,3, 15, 10, 17 to B) because RB are not making. Nor can current pass 19Kfor the same reason. lVhenever RB make, however, coil 10 is energized,motor control switch closes and the fan motor starts. Simultaneouslyholding contact 1213 closes and the circuit for maintaining this contactclosed includes elements r R-. If when the fan is thus running eitherthe room thermostat or the radiator device would move away from theircontacts sufliciently to break either at rb or at R-B, or at bothsimultaneously or either one before the other, the elements 7' R willstill maintain the circuit in closed position and the fan will continueto run. Immediately, however, that either 1 or R break, eithersimultaneously or one before or after the other, the coil 10 will bede-energized and the switch 11 opened to stop the motor.

It will thus be seen that the radiator device dominates the control, tothe extent that no control whatever can be had through the room deviceunless the radiator device is making at both contacts BW'. It will,however, be seen that if the relay circuit has been once closed, one ofthe contacts of each device may open and the circuit still be maintainedin closed condition providing that one element of each device is making.

The construction and Wiring arrangement herein is such that anelectrically operable device, such as a relay or its equivalent, cannever be energized unless all contacts of the control devices are cleanand can make electrical contact, as distinguished from a mechanicalcontact by a dirty contact element, in which latter case no current canpass. As a result, the device provides means whereby if there is not theproper electrical contact, the device cannot be operated at all, andthis is a valuable feature of the invention. Another feature is that,holding contacts are supplied and the arrangement is such that if bothcontacts of one of the devices are electrically engaged and only theholding contact of the other device is engaged and the device isapproaching contact position, and if a vibratory movement causes theelement to engage its contact prematurely to energize the relay orequivalent device, after such engagement and therefore afterenergization of the electrically operable device de energization cannottake place although the last contact to make vibrates considerablybefore it makes its normal contact. Means is thus provided wherebyvibratory disturbance cannot cause the electrically operable device tobe (lo-energized, unless by the natural thermostatic action to break thecontacts.

This holding Assume both contacts of the room thermostat to be closedand assume the radiator device to be warming. Su pose contact R makesand conditions the olding circuit to be held closed after the closing ofthe relay. Then assume R to be near but not yet touch: ing its contact.Then suppose some sufiicient violent vibration which will cause thecontact R to touch its contact before the radiator device issuflicientlv hot to cause the contact to be made naturally. Inasmuch asa holding contact is provided if this radiator device is closed byvibration, the circuit to the relay will be closed and the relay willremain closed. Therefore, except for the holding circuit, the relaywould close on the first tap of the contact R', then open, then closeagain and so on continually in a vibratory manner responsive to theoutside vibratory disturbance. contact arrangement is possible becausethe olding. and making circuits pass through the radiator device withoutany intercommunication. The insulation of the two sequentially makingcontacts obtains. this an ti-vibratory control or makes such a controlpossible, whereby two devices can be used, either being able to causethe relay-to open, but wherein both must cooperate to obtain closure.

Therefore in the present device, in case one of the contacts isdirty nocurrent can pass to the electrically operable device, no matter how manyother contacts are electrically making, and after energization of therelay due to an electricclosu're, energization is maintained if one ofthose contacts which was first to close remains closed.

I claim as my invention: .1. A pair of thermostatically responsivedevices, a relay and source of power in circuit with said devices, eachdevice having two contacts, and a movable member having portionssequentially engageable with said contacts in one order anddisen'gageable in reverse order, and circuit connections such thatenergization of the relay can only be obtained when all contact elementsof both devices are electrically closed, and the arrangement furtherbeing such that after'energization of the relay, due to this closure,energization is maintained,

. if those portions of the movable member of each device whicha werefirst to close remain closed.

device in which the contact portions are insulated from one another.

3. A motor and circuit therefor including a switch, means electricallyenergizable for o eratin the switch, thermostatic switch dethermostaticswitch devices, motor line switch operating means, and holdingcontact,such that all contacts of the pair of switch devices must beelectrically closed to obtain energization of said motorv switchoperating means. 1

4. A motor and circuit therefor including a switch, means electricallyenergizable for operating the switch, thermostatic switch devices eachhaving two contacts and a movable member having portions sequentiallyengageable with the contacts in one order and disengageable therefrom ina reverse order, the contact-engaging portions of one of the switchdevices being insulated from one another,"a holding contact arranged toclose when the motor line switch operating means is energized, andelectrical connections between the contact, movable elements of thethermostatic switch devices, motor line switch operating means, andholding contact, such that all contacts of the pair of switch devicesmust initiallyelectrically close to obtain energization ofsaid motorswitch operating means, and such that as long as at least one contact ofeach of the said thermostatic switch devices is electrically closed suchenergization is maintained.

5. A motor and circuit therefor including a switch, means electricallyenergizable for operating the switch, thermostatic switch devices eachhaving two contacts and a movable member having portions sequentiallyengageable therewith in one order and disengageable therefrom in areverse order, the engaging portions of one of the movable members beinginsulated from one another, a holding contact arranged to close when themotor line switch operating means is energized, and electricalconnections between the contacts 'and movable elements of thethermostatic switch devices, motor line switch operating means, andholding contact, such that all contacts of the pair of switch devicesmust ini tially electricatly close to obtain energization of said motorswitch operating means, and such that, as long as at least one contactof each of the said thermostatic switch devices is electrically engagedsuch energization is maintained, and said holding contact being inseries with one contact of each thermostatic switch device.

6. An electrically energizable switch operating means, thermostaticswitch devices each having two contacts and a movable member havingportions sequentially engageable therewith in one order anddisengageable therefrom in a reverse order, the contactengaging portionsof only one of the switch devices being insulated from one another, aholding contact arranged to close when the switch operating means isenergized, and electrical connections between the contacts and movableelements of the thermostatic switch devices, switch operating means, andholding contact, such that all contacts of the pair of switch devicesmust initially electrically close to obtain energization of saidelectrically energizable switch operating means.

7. A motor and circuit therefor including a switch, and electricallyenergizable switch operating means, thermostatic devices each having twocontacts and a movable member having portions sequentially engageabletherewith in one order, and disengageable therefrom in reverse order, aholding contact arranged to close when the switch operating means isenergized, and electrical connections between the contacts and movableelements of the thermostatic switch device, switch operating means, andholding contact, such that after electrical closure of all but one ofthe contacts of the thermostatic switch devices, a mechanical vibratorydisturbance of that movable member which does not have itscontactengaged, to cause it to alternately engage and disengage itscontact, will not cause deenergization of said electrically energizableswitch operating means.

In witness whereof, I have hereunto set my hand this 20th day ofOctober, 1928.

HAROLD W. SWEATT.

